Revealing nanoscale mechanisms of pyrolysis at phenolic resin/carbon fiber interface

Carbon-carbon composites are a material commonly used in high heat flux heat environments, such as space missions for terrestrial re-entry. Phenolic resins have been used as carbon matrix precursors due to high char yields of 50 - 55%. In this work, molecular dynamics models of a phenolic resin matrix were polymerized and pyrolyzed in the presence of a carbon fiber (CF) surface using experimentally validated protocols to quantify the nanostructural and chemical evolution of the resin matrix as a function of distances from the resin/fiber interface. After pyrolysis, the predicted char yield was 64.2 +/- 0.6%, indicating the presence of the CF surface aids in mass retention relative to a model of a pyrolyzed neat phenolic resin. Ring alignment analyses of the evolving pyrolyzed structures showed signs of templating as rings aligned with the CF surface. Filtering out non-aligned rings revealed bands of charred resin matrix equidistant from one another with similar spacing as that of graphene layers in graphite. The methodology presented helps reveal nanolength scale mechanisms of pyrolysis at resin/fiber interfaces and quantifies microstructural changes difficult to observe in situ, which is important to tailor processing parameters and optimize carbon composite manufacturing.